Difference between Mozilla's new repository and ppa
In the blog post’s comments they already write that it should be introduced for stable releases as well. Does anyone has an idea what the difference between the ppa and the stable releases in the new repository could be and why they introduce a separate repo?
So, in the future: Should I use the new deb repositoy or the ppa? Or does it not make any difference?
It appears to me that the new PPA is for nightly builds, with the sole purpose of facilitating testing of bleeding edge versions.
The PPA that already exists contains Firefox ESR and, since a few years, also stable regular releases.
So I think your choice is clear. Unless you want to contribute to Firefox by testing development versions, you should stick to the "Firefox ESR and Thunderbird stable builds" PPA.